This invention relates to a system and method to indicate to a pilot the maximum safe altitude to which he may fly an airplane with any given batch of fuel, regardless of the range of parameters of that fuel. The problem of fuel vapor lock in aircraft fuel systems and of pneumatic lock in aircraft carburetors is one that goes back to the early days of aviation. Gasoline is a volatile fluid which is subject, when used in airplanes, to conditions of rapid changes in pressure and temperature. As a result, vaporization and cavitation can take place in the lines and/or in the fuel pumps and fuel foaming or boiling (pneumatic lock) can take place in the carburetor. Either of these conditions can cause a loss in engine power with potentially catastrophic results.
These problems were originally dealt with by lowering the vapor pressure of the fuel to the lowest possible level while improving fuel system design. Typically, aviation gasoline has had a Reid vapor pressure (RVP) of 7 to 8 in an effort to offset the problem of vapor and pneumatic lock. Therefore, general aviation (G.A.) aircraft are certificated with this fuel, and must be recertificated if a fuel with a RVP higher than this is to be used.
In the early 1980's, as the availability of aviation fuel declined while its price increased, a gradual shift to the use of automotive fuel in aircraft took place. In addition, in more recent years the need to meet EPA requirements regarding the elimination of lead and other pollutants has forced refiners to experiment with new blends of aviation fuel. In order to provide some flexibility for the refiners, the maximum RVP of the new fuels was raised to 13.
It can be seen from the above that each airframe type originally certificated on aviation fuel with 7 to 8 RVP would have to go through a flight test program on 13 RVP fuel. Given the large number of airframes which would have to be recertificated, the test program approach would be costly and time consuming. A method of avoiding the need to evaluate each airframe would be a significant advance in the art.